The present invention relates to an electrochemical sensor.
Electrochemical sensors are described, for example, in the Automotive Electronics Handbook (1994), chapter 6, Wiedenmann et al., xe2x80x9cExhaust Gas Sensorsxe2x80x9d, for application in exhaust gas analysis of internal combustion engines. Such sensors include a sensor element having at least one signal forming electrode, in which, because of the sensitive properties of the sensor element, a current flows which can be used to determine the concentration of at least one exhaust gas component. Furthermore, the sensor element has at least one electrical element, such as a heater or another electrode, whose potential is clearly different from that of the signal-forming electrode and which is separated from a supply lead of the signal-forming electrode by an insulating layer or an insulating body, for instance a solid electrolyte layer.
The disadvantage of the known sensor is that a fault current into the supply lead of the signal-forming electrode can occur, when the insulating effect of the insulating layer or the insulating body is insufficient because of the potential difference between the signal-forming electrode and the electrical heating element, whereby the measuring signal is corrupted.
To avoid the influence of fault currents into the supply lead of the signal-forming electrode, it was suggested in German Patent Application No. 198 57 468.1 that an electron-conducting intermediate layer be provided between the heater and the signal-building electrode. In this connection, the electron-conducting intermediate layer does not completely separate the heating element from the signal-forming electrode, so that the fault current can be only partially drained off via the electron-conducting intermediate layer. Fault currents can also arise from further electrical elements, which also have a non-neglectable potential difference from the signal-forming electrode, and which are positioned, for example, between the electron-conducting intermediate layer and the signal-forming electrode.
Compared to the related art, the electrochemical sensor of the present invention has the advantage, that fault currents occurring in the sensor are absorbed by shielding. Thus, the current flowing in the supply lead of the signal-forming electrode, by which the concentration of an exhaust gas component is determined, is not corrupted, making a more precise and uniform functioning of the sensor possible.
The present invention achieves that fault currents flowing in or on the sensor element into the supply lead of the signal-forming electrode can be reduced or avoided by having the fault currents drain off via the shielding.
According to the present invention, it is achieved that at least the predominant part of the fault currents on or in a bonding device which electrically connects the supply lead of the signal-forming electrode via a first conductor element, and the electrical element via a second conductor element by way of at least one cable proceeding from the sensor, are drained off via a shielding printed circuit trace provided on or in the bonding device.
Since the signal-forming electrode and the shielding are at an at least similar potential, it is also achieved that zero or only low currents can flow between the shielding and the signal-forming electrode, even in the presence of an otherwise insufficient insulation between the signal-forming electrode and the shielding.
If the shielding is at an at least close to constant potential, then a possibly appearing low fault current into the signal-forming electrode is at least nearly constant, and therefore easy to correct by an outer protective circuit.
An additional advantage accrues if the shielding is short-circuited with a further electrode which does not take part in the determination of the concentration of the gas component by a current flowing in it, and whose potential lies at least close to the potential of the signal-forming electrode. This has the positive effect that bonding of the shielding can be done away with in the connecting side region of the sensor element.
Because the shielding forms a supply lead of the further electrode, the printing step for the supply lead of the further electrode can also be eliminated.